14 replies to this topic

[elcid79]

Hello,

Sorry if this is a dumb question.  I am new to telescopes, as this is my first.  I am generally pretty handy with technology but this has me stumped.   My Evolution Alt/Az mount keeps missing its GoTos.   

It is worst if I swing from one pole to another, or move around a fair bit.   But it seems to just not want to center on objects.  Even with my 32mm plossl and 40mm, often it completely misses.  Tonight, it missed the moon.  Further when I centered on known objects (sirius) and attempted to add them to my alignment, it said that they were too far out of location.

 

Align Process.

Either with HC using city and date information, or on tablet through skysafari (gps) both have the same problem.

Step one, level the telescope (the ball level is perfectly flat.) and put it on celestron antivibration pads on solid driveway. 

Center on first star with wide field eyepiece.  Change to the 13mm center with the last movement up and to the right.  Align star one.  Move to star two, and follow the same process, as well as with star 3.  I am pretty meticulous about it.   After doing this, I get an alignment successful message.  If I jump back and forth to close by stars it seems to be okay, but if I swing about 90(ish)* or more, that is when it starts to fail.  I will tell it to go back to one of my alignment stars and it will completely miss.  If I look at my red dot finder, it will be well off of the target.         

It works the same with Sky Safari, and the HC.   It will initially appear to be okay, I can bounce around a bit, but eventually (and quickly) it starts missing objects, particularly when swinging from one pole to the next.   

How accurate are these goto's supposed to be?

Observations - This is a consistent issue, that I originally thought was associated with my ipad going to sleep.    I disabled the sleep function, and attempted it with the hand control, neither of these helped.

Slop (I think you call this backlash) - Altitude adjustments are instantaneous, in both directions even at low levels like 2.  Azimuth has a noticeable delay (8 seconds or so) at lower speeds when changing directions left to right.

I have attempted to adjust the backlash on azimuth and have reduced it to around 3-4 seconds.  While utilizing a lot of the available backlash slider.

Lastly, the azimuth adjustments make squeek squeek sound when at low speed.  Altitude does not do exhibit this.      

I am running the latest firmware.

Thanks in advance.

 

John

Edited by elcid79, 23 January 2022 - 06:06 PM.

[Noah4x4]

This was my early experience until I realised my skill in judging the centre of an eyepiece was poor. This is common. A 12mm cross hair reticle eyepiece can help. If you don't have one, try defocusing your stars until they look like a doughnut (US 'Donut'). It is easier to centre that doughnut accurately with reference to the perimeter of the eyepiece.

Selecting the right pair of stars can help. I found selecting two 90° apart and either side of a line North -South helped (so don't select Polaris).

What you are GoingTo can be material. Planets are notorious for retrograde movement.

Try using Longitude and Latitude rather that City. I am 52 miles from 'London', and that was sufficient to throw me out.

To be honest, despite all the above improving things, I was never guaranteed a perfect alignment and spot on GoTos until I added Starsense, then properly calibrated that, and added ten additional alignment points across the sky and seasons. Its platesolving is much more accurate than my old eyes. However, I believe the additional alignments points are key. These act like SYNC offering the scope more reference points. You say your GoTos are worse the further away from your start point. Try picking sky zones to observe (example Orion). Use stars in that same zone. Never use planets or DSOs, use only stars.

This can be very frustrating for beginners, it took me a long time to get this right using any method. Mike Swansons book (Nexstar Users guide) probably has more tips. You should at least be able to get star targets into a 32mm or 40mm eyepiece. But don't ever expect perfect spot on GoTos in a 13mm at f/10.

Edited by Noah4x4, 23 January 2022 - 02:35 AM.

[GoFish]

Two things to offer:

1. I never felt my tripod legs were very well “stuck” to the anti-vibe pads. They slid around on them easily. So now I use the pads only with manual pointing scopes, where I don’t care if the tips of the legs might slip a little. 
2. The amount of backlash you reported in azimuth sounds excessive. And the noise adds to my suspicion that there may be a mount mechanical problem. 

[Michael_Swanson]

The amount of backlash in azimuth is definitely not correct.  Maybe the clutch isn't tight?  If it is (and it sounds like you would not miss this detail), I recall a post here on Cloudy Nights showing disassembly of the mount to discover a set screw associated with the clutch was loose.  

 

That said, since it is new, you may want to contact your dealer for a replacement or Celestron for warranty work.

 

Best regards,

Mike Swanson
https://www.NexStarSite.com

[Procyon]

Just in case, you have daylight saving time on/off on the setting yes?

[sanbai]

As Mike said, my first idea is that the clutches are not tight. They don't need to be super tight, but check they aren't loose.

Other that that, your procedure looks fine to me.
Check this:
align as usual
Go-To a nearby object. Do not correct, just look.
Check what you see exactly.
Go to somewhere else, far away (you can test both by go-to and manual slewing for this step). No need to look.
Go back to the initial object.
Do you see the same?



Santiago

[elcid79]

Thanks for the recommendations.  The clutches were tight.  I checked last night and again just now.   When I did the step procedure down to 12mm, I did defocus the stars on several of my attempts with the same end result.  One thing I notice if I grab the base, I can wiggle the entire top part of the mount, the lower part which screws to the tripod is secure, but i can wiggle the fork upper assembly.  The OTA / Alt arm is snug with no movement with the same pressure applied.

Daylights savings is off. 

 

I used GPS when aligning with the app and double checked the coordinates.  I used city when aligning with the HC just to try something different.

If the weather is good tonight, I will try Santiago's recommendation.  Align and slew and back to the same star, to see if it still exhibits this.

Lastly, I spoke with the retailer, they offered to set up an exchange.  If I can't figure it out tonight (it looks like it may be clear again)  I will set it up tomorrow.

Any other thoughts?  

Edited by elcid79, 23 January 2022 - 11:57 AM.

[elcid79]

I verified the backlash issue with the hand controller just now.  Using a stopwatch.

 

When changing directions with HC slew speed at 4 it takes 5 seconds for the scope to start moving, fairly consistent left to right.  With HC speed set to 3 it takes 10 seconds.  For reference the Alt rate is about 1 second at HC 3.   The retailer set up an exchange.  

[elcid79]

https://youtu.be/m5v2TlBMJ-A

I made a video of it, the initial scroll was fast because that was the direction it had previously moved in.  When I switch directions you can see the backlash.   This is with the hand controller Speed 4 then 3.

[carver2011]

From your YouTube, that is much too much backlash. The is a backlash adjustment you can do. check Mike Swanson's NextStar Resource site.

[carver2011]

From your YouTube, that is much too much backlash. There is a backlash adjustment you can do. check Mike Swanson's NextStar Resource site.

Edited by carver2011, 23 January 2022 - 06:43 PM.

[elcid79]

If I set the backlash compensation up to 50% it reduces it to about 3.5-4 seconds at lvl 4. Beyond that it doesn’t improve. Even at that it makes it a bit stuttery.  During daylight tomorrow morning I will take it back outside and make another daylight video. 

I have had slightly more success this evening. I removed the anti vibration pads. What I have noticed is if I slew a full 360 it gets way off. If I go back the opposite direction it is closer to target. Tonight I appear to have been able to keep it in the eyepiece for the most part. I haven’t had to re-align, it has been usable. Yet still not particularly consistent.  A few stars missed entirely, but were close enough tonight that I could see the glow and was able to find it.  Except for this odd behavior tonight that I didn't experience in the past was it completely missed a few stars.  But then started working again?  Without adding aditional stars, or re-aligning.   I didn't change anything at all.  Just slewed somewhere else, poked around a bit, then came back.  If I slewed off, and then back immediately, it did not work and returned to the original dark spot.  It is always pointing in the general direction and seems to know what it wants to do, just can't get across the finishline.   Perhaps the azimuth gear is what is messed up / inconsistent.   

Tracking seemed to be good today, I left it for about 30-45 minutes, when I went back the star was still centered.  I am still concerned about the backlash, but I don't want to unnecessarily return this one, and replace it if it's not messed up.   

Edited by elcid79, 23 January 2022 - 08:43 PM.

[Michael_Swanson]

There is definitely something wrong with the azimuth axis.  Most likely a loose bolt.  Since it is under warranty, I would not recommend repairing it if you can get it replaced by your dealer or if you dealer will work with Celestron on the warranty repair.

 

Best regards,
Mike Swanson
https://www.NexStarSite.com

[elcid79]

Thanks Mike. They set up an RMA and are going to send a new one. I appreciate the help.

J

[elcid79]

Well the saga continues.   My replacement scope arrived on friday and the shipping box had quite a bit of damage.   It all looked isolated to the OTA area and after carefully checking it out, and pouring over it, I decided that it was not damaged.  The image was super clear, so I was pretty excited.   Well tonight I put the mount through its paces and this happened.    I will likely create a new thread, because its a new issue.  But I figured I would post the video here. 

https://youtu.be/vs_bQuuqSEo